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The high-field magnetoresistance of polycrystalline manganites of varied composition in magnetic fields up to mu(sub 0)H=47 T is analyzed. The observation of a systematic correlation between grain-boundary magnetoresistance and bulk Tc indicates that magnetic order at grain boundaries is governed by parameters such as doping and average ionic size.

A modified melt-texture process was used to prepare a bulk melt textured YBCO material that features single-domain grains of as much as 35 mm in diameter. The material exhibits a weaker trapped field dependence and higher trapped field values at temperatures ranging from 55 and 75 degrees Kelvin. A strong pinning in the derived superconductor material is suspected because of a pronounced peak effect discovered in the field dependence of the critical current density.

A study was conducted on the influence of mechanical deformation on the critical current density and irreversibility characteristics of Bi-(Pb)-Sr-Ca-Cu-O superconducting tapes. Results reveal that hot pressing enhances critical current density in the low field region by improving grain connectivity and grain alignment. Hot deformation, however, was found to benefit only weak links.

The effects of Fe, Zr and Cu substitution on the microstructure and formation of crystallographic texture were examined. The melt-spun SmCo8.5 and Sm(Co0.9Fe0.1)8.5 ribbons exhibited a high degree of texture with the easy magnetization axis parallel to the longitudinal direction of the ribbons.

The metamagnetic compound La1.2Nd0.2Sr1.6Mn2O7 was examined as a polycrystalline material, and its magnetization and magnetoresistance results are presented.

The properties of bulk melt-textured [YBa.sub.2][Cu.sub.3][O.sub.7-[Delta]] disks have been investigated with respect for use as trapped field magnets. Large single-domain disks up to 35 mm in diameter and 12 mm in thickness were obtained by a melt-texturing process. The trapped field in the 1 mm gap between two single-domain disks was found to increase from 1.2 T at 77 K up to 9.0 T at 47 K which is the highest trapped field achieved in non-irradiated samples. The trapped field at lower temperatures is limited by the mechanical strength of the material for which a value of 25 MPa was estimated. We observed an exponential decrease of the trapped field with increasing temperature, which can be explained by flux creep in the framework of collective pinning. The activation energy for this process was determined by relaxation measurements. Index terms - Critical current density, flux creep, high-[T.sub.c] superconductors, superconducting permanent magnets.

Compounds having copper oxide layers can become superconductors when doped, and they show almost two-dimensional quantum antiferromagnetic behaviour. Novel results on the magnetic properties of Ba(sub3)Cu(sub2)O(sub4)C1(sub2) and Ba(sub2)Cu(sub3)O(sub4)C1(sub2) are reported. The crystals were prepared by flux methods and magnetic measurements performed in a Quantum Design superconducting quantum interference device magnetometer.

The low-field magnetoresistance (MR) effect in polycrystalline thin films at T

The disproportionation of Sm(sub2)Fe(sub17-x)Gax was investigated in order to apply the hydrogenation-disproportionation-desorption-recombination (HDDR) process of Sm(sub2)Fe(sub15)Ga(sub2)Cy, which has good magnetic properties and high thermal stability. HDTA samples showed a decreasing content of the 2:17 phase for rising hydrogen pressures. A nearly full disproportionation can be achieved.

Die-upset experiments on hot compacted commercial melt-spun powders MQP-A and MQP-B were carried out under an argon atmosphere at 500 to 800 [degrees] C with strain rates of [10.sup.-4] to [10.sup.-1] [s.sup.-1]. The kinetic analysis of the strain-rate stress relations yields the following dependences for the strain rate: (i) on flow stress, a power law with a stress exponent of 3, (ii) on temperature, a thermal activated process with activation energies of 280 and 400 kJ/mol for the MQP-A and -B samples, and (iii) on mean grain size, a reciprocal proportionality for MQP-A. These results indicate an interface-controlled solution precipitation process as the microstructural mechanism of hot deformation and texturing. Hereby the grain-boundary phase seems to be not required to be in the liquid state for deformation. Its presence is necessary for a crack-free deformation at high strain rates. In the case of radially textured ring magnets made by backward extrusion an area reduction of about 65% is necessary for optimization of the needed press stresses as well as the magnetic properties. Typical values are [B.sub.r] = 1.25 T, [[Mu].sub.0][H.sub.cj] = 1.1 T and [(BH).sub.max] = 280 kJ/[m.sup.3].

Ball milling increased the coercivity of Sm2Fe17N(x) permanent magnets from 0.3 to 1.5 T. Magnets subjected to long-term milling comprised isotropic polycrystalline grains with small grains and single domain particles. Coercivity was a necessary and permanent magnet property of Sm2Fe17N(x).

An investigation of the magnetization, magnetic susceptibility, and resistivity for Cr-doped p type and Ni-doped n type FeSi2 single crystals is carried out. The results of resistivity measurements are analyzed within a framework of different hopping conductivity models.

A study was conducted to investigate the temperature and magnetic field dependence of Hall effect, the magnetization and the resistivity of Mn-doped beta-FeSi2 single crystals in the temperature range of 4-300 K in magnetic fields up to 5 T. The result reveals the negative magnetoresistance and strong nonlinear magnetic field dependence of the Hall resistivity and magnetization.

The epitaxial trilayer consisting of hole and electron doped manganites on either side of an insulating SrTiO3 barrier is fabricated, which exhibits strong diodelike I-V characteristics at room temperature. It is fund that the asymmetry in the I-V curve disappears at low temperatures owing to the insulator to metal transition.

The magnetic properties of [Nd.sub.16.2][Fe.sub.78.2][B.sub.5.6], [Nd.sub.12.6][Fe.sub.81.4][B.sub.6.0] and [Nd.sub.12.6][Fe.sub.69.4][Co.sub.11.0][Ga.sub.1.0][B.sub.6.0] alloys after the application of modified HDDR (hydrogenation-disproportionation-desorption-recombination) procedures have been investigated and particular emphasis has been given to the development of magnetic anisotropy and high coercivity in these different types of materials. Conventional HDDR processing leads to anisotropic material only in the case of the [Nd.sub.12.6][Fe.sub.69.4][Co.sub.11.0][Ga.sub.1.0][B.sub.6.0] alloy. Combining solid-disproportionation with a controlled recombination under partial hydrogen pressure at 900 [degrees] C, a significant degree of anisotropy and a good coercivity were achieved for the two ternary alloys. These findings indicate the possibility of more than one mechanism and the relevance of the rod-like solid-disproportionated structure for the inducement of anisotropy. Another modification of the standard procedure, the reactive milling technique, leads to isotropic [Nd.sub.16.2][Fe.sub.78.2][B.sub.5.6] powder with grain sizes, both in the disproportionated and recombined states, significantly smaller than those of conventional powder and a very high coercivity of [[Mu].sub.0J][H.sub.c]=1.88T. Index Terms--HDDR, magnetic anisotropy, NdFeB, reactive milling

Investigates the temperature and field dependence of the magnetoresistivity and magnetization of melt-spun ribbons with nominal composition. Experimental procedures; Findings and analysis of results.